Question: On the first 6 tests of his history class, Kevin got an average score of 81. What does he need on the next test to have an overall average of 83?
Answer: Let his score on the next test be $x$ The sum of all of his scores is then $6 \cdot 81 + x$ The same sum must also be equal to $7 \cdot 83$ Solve: $x = 7 \cdot 83 - 6 \cdot 81 = 95$.